Historical and Current Distribution of Eelgrass in Long Island Sound
The history of eelgrass begins long before anyone mapped its distribution.
Eelgrass was abundant before 1930.
We must read historical maps of eelgrass counterintuitively. We know that eelgrass was abundant in Long Island Sound before 1930 because of the ubiquitous use of eelgrass as insulation, roof thatching, mulching, etc. Construction workers used eelgrass as insulation and soundproofing in Radio City Music Hall and Rockefeller Center [1].
Eelgrass was so common that it was not noteworthy on historical maps. That’s why our maps pre-1930 have few data points. If something is commonplace, then people are unlikely to record it. So we must infer that eelgrass was common throughout Long Island Sound. Figure 1 demonstrates the observations of eelgrass before 1930.
Figure 1: Historical eelgrass distribution before the 1930s wasting disease epidemic [2]
The wasting disease epidemic that began in 1930 awoke scientific interest in eelgrass. Scientists wanted to know what had caused this massive die-off and if it could be prevented from happening again.
The wasting disease of 1930
A global epidemic affecting eelgrass in the Atlantic Ocean began in 1931; a slime mold pathogen was the likely culprit [3, 4, 5]. It spread across the Northeast and killed nearly all the eelgrass in its path. In the early 1930s, sea temperatures were abnormally high, which made eelgrass more susceptible to the pathogen. By 1933, approximately 1% of the original eelgrass population remained.
Low-salinity areas retained some of their eelgrass since the slime mold pathogen creates fewer negative symptoms in areas with 10% salinity or less [6, 7].
When fresher water gave eelgrass the chance to rebound, it was foiled in the western reaches of Long Island Sound due to massive population increases in the watershed.
Eelgrass recovered partially before experiencing further complications.
Eelgrass began a promising recovery from the slime mold pathogen by the mid-1930s. Reports written during that time found that seeds were free of wasting disease symptoms and cellular slime mold [8]. Eelgrass began a patchy but strong recovery in the eastern part of Long Island Sound from Clinton Harbor and eastward.
By the 1990s, a clear trend emerged. Areas west of Old Saybrook either had not recovered from the wasting disease or had very unhealthy eelgrass populations. Even in the eastern part of Long Island Sound, the Niantic River experienced a patchy recovery followed by a steep decline. The poor rebound in the Niantic River and the western parts of Long Island Sound is attributed to nitrogen pollution from increased human populations in the watershed and less available light. The depth of eelgrass changed by the end of the 1990s; coastal construction decreased light availability leading to eelgrass inhabiting shallower depths.
Figure 2: The watershed for Long Island Sound is depicted in green. Water from Canada to Long Island drains into the sound. PC: Long Island Sound Study
Fishers Islands has the largest, most healthy beds of eelgrass in NY.
Eelgrass is scarce in Long Island Sound.
Ariel survey is a broad-scale method to assess the position and abundance of eelgrass in Long Island Sound. The most recent survey, completed in 2017, shows a continuing decline from previous years (figure 3).
All the eelgrass is in the easternmost parts of the sound, mostly in Connecticut and Fishers Island, NY.
Figure 3: Current (2017) distribution of eelgrass mapped by the 2017 Ariel Long Island Sound Survey
Restoration projects around Long Island Sound are trying to bring back eelgrass to viable waters.
Restoration is critical.
Seagrass restoration projects do not have a glowing track record. These projects are costly and are not often successful [9], but with careful evaluation and tenacity come innovative techniques.
Jamie Vaudrey is one of the dedicated scientists involved in these restoration efforts. She has created a tiered system (figure 4) to target where restoration efforts for eelgrass should begin. She has also identified areas of Long Island Sound that require more ecological work to restore water quality before restoration efforts can be successful.
Figure 4: Restoration analysis shows areas where eelgrass habitat is most suitable in dark green and least in dark purple [10].
The eelgrass on Fishers Island is strong and vital to the restoration efforts around Long Island Sound.
Vital eelgrass beds.
The 2017 survey showed us that eelgrass beds are retreating in Long Island Sound. Fishers Island is home to nearly all of New York’s eelgrass. Efforts to restore it are not succeeding fast enough, and rising sea temperatures make Long Island Sound waters even less habitable.
Fishers Island is a critical source of seeds for these restoration projects. We may still have hope that Long Island Sound can become a thriving, habitable environment for eelgrass if scientists can discover a suitable restoration technique. Without restoration, sea temperatures will rise too quickly for Long Island Sound eelgrass to adapt. Then we will lose all of our eelgrass, including Fishers Island.
Figure 5: Current (2017) distribution of eelgrass mapped by the 2017 Ariel Long Island Sound Survey zoomed in to display Fishers Island, NY and Connecticut.